Background For Teachers:Water is constantly moving from one location to another and changing state. Snow and rain fall to Earth from clouds. This is called precipitation. The rain water and melted snow run downhill into rivers and lakes, sometimes crashing over waterfalls. Eventually the water flows into evaporation basins such as the ocean or the Great Salt Lake, where water can return to the atmosphere.

As water evaporates, it changes from liquid into gas, and moves from oceans, lakes, and rivers into the atmosphere where it forms clouds. Then the cycle begins all over again. (Refer to Instructional Procedures for a discussion on how clouds are formed.)

Review with the students what is needed for water vapor to condense back
to water. (They may bring up a cool mirror, cold pitcher with ice water, cool
ground, cold window, etc.)

Review with the students why the water vapor condenses on these surfaces.
(The warm air has water vapor in it. When it comes in contact with something
cool or cold, the water vapor condenses on the cold surface.)

Take the students outside on a semi-cloudy day. Discuss with them that clouds
are made up of small water droplets that have condensed from water vapor.
Relate the following: “We know that warm air with water vapor in it needs to
come in contact with something cold to condense into water droplets. What is it
that water vapor comes in contact with high in the atmosphere to condense into
a cloud?”

After a few guesses, teach the students that as water vapor cools in the higher
atmosphere, it is attracted to dust particles that are present in the atmosphere.
When the cooled water vapor comes in contact with the dust particles, the water
vapor will condense into a cloud.

The amount of water vapor and dust in the air and where the cold air is in the
atmosphere will determine the types of clouds that are formed.

Instructional Procedure
(This is a teacher demonstration for a student inquiry discovery.)

Have the students write in their journal.

Tell the students that you (the teacher) are going to make a cloud in a bottle.
You will also give some explanations while doing the experiment. Have them
answer any questions you may ask during the demonstration.

Get a two-liter bottle with a lid.

Add 1/2 cup of luke-warm water. Ask: “Why is water added to the bottle?”
(Water is needed to make clouds.)

Light a match and have it burn down the wood a little bit. Blow it out. As soon
as it is blown out, quickly place the smoldering match into a bottle to add some
smoke to the bottle. (Do this twice.) Ask: “Why is smoke added to the bottle?”
(When the water vapor cools it needs dust particles to collect onto to make a
cloud.)

Seal the bottle with the lid.

Shine a flashlight through the bottle and have students record in their journals
what they see.

Explain to the students that in a minute you are going to squeeze the bottle as
hard as you can for 60 to 90 seconds. The pressure in the bottle will cause the
temperature to rise in the bottle. Ask: “What is going to happen to some of the
water in the bottle as the temperature rises?” (Some of the water will evaporate
putting water vapor into the air.)

Begin squeezing the bottle. As you are squeezing the bottle explain that after 90
seconds you are going to release your squeeze. Releasing the squeeze is going
to cause a pressure change. A rapidly decreasing pressure change in the air
always causes a lower temperature. Ask: “What is going to happen to the
water vapor in the bottle when the pressure is released?” (The water vapor will
cool down and collect onto the dust causing a cloud.

Release your squeeze. As the pressure is quickly released, a cloud will
momentarily form. Shine the flashlight in the bottle again. Have the students
write in their journals what they observed. (A cloud formed.)

Let the bottle sit for a couple of minutes. Shine the flashlight in the bottle again.
Have the students write what they observed and why they think this happened.
(The cloud disappeared because the air became warm and the cloud evaporated
into water vapor again.)

Discuss the questions you asked during the demonstration.

Discuss how this model represents the water cycle.

Extensions:

Science-

As time permits, investigate the variables. Try the activity again, each time
omitting one of the factors (humidity, an air pressure decrease causing a
temperature drop, and particles in the air) and see if a cloud still forms. (ILO 1)

Have students suggest other forms of dust (i.e., chalk dust). Some students may
want you to try the experiment without any dust. (ILO 1)

Homework & Family Connection
Give each student the assignment to teach his/her family how clouds are formed.
He/she should be able to explain with these words:

Source of water

High Pressure (heat)

Evaporation

Dust particles in the air

Change of air pressure (cooling)

Cloud forms (condensation)

Have the student explain the experiment that was done in class by using a two-liter
bottle as a prop only, showing what was done to the bottle to make a cloud. Have him/her
report back to class of his/her success.

Assessment Plan:Check for students’ understanding by looking at their journals. See how well hey
answered your questions during the demonstration. Listen to their answers th discussion
for understanding.